Apparatus and method for direct injection of additives into a polymer melt stream

ABSTRACT

This invention provides an apparatus and method for injecting an additive directly into a polymer melt stream. The method comprises supplying a melt flow of a polymeric host material to a die assembly having a thin-plate assembly and injecting at least one additive into at least one predetermined location in a cross-section of the melt flow of the polymeric host material while the melt flow passes through the die assembly. The method achieves uniform dosing of the one or more additives in the extrusion direction in the polymeric host material without homogeneously mixing the one or more additives and the polymeric host material. The apparatus for directly injecting one or more additives into a polymer melt stream comprises a pumping system, a die assembly having a thin-plate assembly, and a distribution line.

FIELD OF THE INVENTION

[0001] This invention relates to the introduction of additives into apolymer. More specifically, this invention relates to an apparatus andmethod for the direct injection of additives into a polymer melt stream.

BACKGROUND OF THE INVENTION

[0002] The addition of additives to molten polymers has beenaccomplished by several means. One such means is blending the additivesand the polymer chips together in the polymer chip dryer or in thestorage hopper prior to extruding the polymer chips and the additivesinto strands for pelletizing. Another method for introducing additivesinto a polymer melt stream is to inject the additives at the throat, themixing zones, or the vent of the extruder and to allow the extrusionprocess to fully blend the additives into the polymer components. Athird method of introducing additives into a polymer melt streaminvolves injecting the additives into static mixing elements locateddownstream of the extruder to fully blend the additives into the polymercomponents.

[0003] Problems arise, however, in that some additives may be heatsensitive and may also cause polymer degradation or other undesirablereactions with the polymer if blended with the polymer before extrusioninto polymer strands. Moreover, some additives such as, for example,zinc stearate, can cause extruder screw slippage.

[0004] A way to overcome such problems is to introduce the additivesinto a polymer melt stream after extrusion of the polymer into strandsfor pelletizing. One such method is to coat the polymer pellets with theadditives after the polymer extrusion process has occurred. A problemarises, however, in that for additives that amount to less than about 1percent of the concentration of the total polymer product, this methoddoes not generally result in a good uniform dosing of additive topolymer.

[0005] A need, therefore, exists for a method of introducing additivesinto the polymer that overcomes the above-discussed limitations.

SUMMARY OF THE INVENTION

[0006] It is a primary object of the present invention to introduce oneor more additives directly into a polymer melt stream.

[0007] Another object of the present invention is to strategically placeone or more additives at specific locations within an extruded polymerstrand using a thin plate die assembly.

[0008] Thus, according to one embodiment of the present invention, thereis provided a method of directly injecting one or more additives into apolymer melt stream comprising the steps of supplying a melt flow of apolymeric host material to a die assembly having a thin-plate assemblyand injecting at least one additive into at least one predeterminedlocation in a cross-section of the melt flow of the polymeric hostmaterial while passing the melt flow of the polymeric host materialthrough the die assembly. The one or more additives is injected into oneor more exact locations within the cross-section of the polymeric hostto achieve uniform dosing, in the extrusion direction, of the one ormore additives within the polymeric host material without homogeneouslymixing the one or more additives and the polymeric host material into asingle phase.

[0009] According to another aspect of the present invention there isprovided an apparatus for carrying out the direct injection of one ormore additives into the melt flow of a polymeric host materialcomprising a pumping system, a die assembly having a thin-plateassembly, and a distribution line.

[0010] According to yet another embodiment of the present inventionthere is provided a method of making pellets from polymers comprisingthe steps of supplying a melt flow of at least one polymeric hostmaterial to a die assembly comprising a thin-plate assembly, directingthe injection of at least one additive into at least one predeterminedlocation in a cross-section of the melt flow while passing the melt flowthrough the die assembly to form strands, and cutting the polymerstrands into pellets. The resulting pellets have a precise amount ofadditive dosed at the at least one predetermined location in thecross-section of the polymeric host material. The uniform dosing of theone or more additives is achieved without homogeneous mixing of theadditive and the polymeric host material.

[0011] By precisely injecting low concentrations of one or moresensitive polymer additives into the polymeric host material at the die,degradation and chemical reactions in the extruder are avoided, handlingof additive material is simplified, and uniformity of the additive inthe strand of polymeric host material is improved. Moreover, accurateplacement of additives in the cross-section of a strand of polymerichost material is achieved.

[0012] The above and other objects, effects, features, and advantages ofthe present invention will become more apparent from the followingdetailed description of the preferred embodiments thereof, particularlywhen viewed in conjunction with the accompanying drawings wherein likereference numbers in the various figures are used to designate likecomponents.

BRIEF DESCRIPTION OF THE DRAWINGS

[0013]FIG. 1a is a schematic of the apparatus of the present invention.

[0014]FIG. 1b is a schematic of an alternate pumping system useful inthe apparatus of the present invention.

[0015]FIG. 1c 1 b is a schematic of a second alternate pumping systemuseful in the apparatus of the present invention.

[0016]FIG. 2 is an exploded view of one configuration of the thin-plateassembly in the die assembly used in the apparatus of the presentinvention.

[0017]FIG. 3 is an exploded view of a second configuration of thethin-plate assembly in the die assembly used in the apparatus of thepresent invention.

[0018]FIG. 3a is a schematic diagram of one of the plates of thethin-plate assembly shown in FIG. 3.

[0019]FIG. 4 is an exploded view of a third configuration of thethin-plate assembly in the die assembly used in the apparatus of thepresent invention.

[0020]FIG. 4a is a schematic diagram of one of the plates of thethin-plate assembly shown in FIG. 4.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0021] To promote an understanding of the principles of the presentinvention, descriptions of specific embodiments of the invention follow,and specific language is used to describe the same. It will neverthelessbe understood that no limitation of the scope of the invention isintended by the use of this specific language and that alterations,modifications, equivalents, and further applications of the principlesof the invention discussed are contemplated as would normally occur toone of ordinary skill in the art to which the invention pertains.

[0022] In one embodiment, the present invention is a method of directlyinjecting one or more additives into a polymer melt stream. The methodcomprises the steps of supplying a melt flow of a polymeric hostmaterial to a die assembly having a thin-plate assembly and injecting atleast one additive into at least one predetermined location in across-section of the melt flow of the polymeric host material whilepassing the melt flow of the polymeric host material through the dieassembly. The one or more additives is injected into one or more exactlocations within the cross-section of the polymeric host to achieveuniform dosing in the extrusion direction of the one or more additiveswithin the polymeric host material without homogeneously mixing the oneor more additives and the polymeric host material into a single phase.

[0023] In another embodiment, the present invention is an apparatus fordirectly injecting one or more additives into a polymer melt stream. Theapparatus comprises a pumping system, a die assembly having a thin-plateassembly, and a distribution line. The apparatus of the presentinvention is designed to inject one or more additives into the melt flowof a polymeric host material at one or more specific locations in thecross-section of the polymeric host material as the polymeric hostmaterial passes through a die assembly and is shaped into polymerstrands. While the resulting pellets have a precise amount of one ormore additives dosed at one or more specific locations of thecross-section of the polymeric host material, the polymer and the one ormore additives are not homogeneously mixed as a single phase.

[0024] In yet another embodiment, the present invention is a method ofmaking pellets from polymers comprising the steps of supplying a meltflow of at least one polymeric host material to a die assemblycomprising a thin-plate assembly, directing the injection of at leastone additive into at least one predetermined location in a cross-sectionof the melt flow while passing the melt flow through the die assembly toform strands, and cutting the polymer strands into pellets.

[0025] Virtually any suitable polymer may be usefully employed in thepractice of this invention. In this regard, suitable classes ofpolymeric materials that may be employed in the practice of thisinvention include polyamides, polyesters, polystyrene, acrylics,polyolefins, and combinations thereof

[0026] One particularly preferred class of polymers useful in thisinvention is polyamide polymers. In this regard, those preferredpolyamides useful in the practice of this invention are those that aregenerically known by the term “nylon” and that are long chain syntheticpolymers containing amide (—CO—NH—) linkages along the main polymerchain. Suitable polyamides include those polymers obtained by thepolymerization of a lactam or an amino acid and those polymers formed bythe condensation of a diamine and a dicarboxylic acid. Examples ofparticularly useful polyamides are nylon 6, nylon 6/6, nylon 6/9, nylon6/10, nylon 6T, nylon 6/12, nylon 11, nylon 12, nylon 4/6, andcopolymers or mixtures thereof. Polyamides can also be copolymers ofnylon 6 or nylon 6/6 and a nylon salt obtained by reacting adicarboxylic acid component such as terephthalic acid, isophthalic acid,adipic acid, or sebacic acid with a diamine such as hexamethylenediamine, methaxylene diamine, or 1,4-bisaminomethylcyclohexane. Mostpreferred is nylon 6. The polymers are generally supplied in the form ofpowders, chips, or granules.

[0027] Additives that may be injected according to the present inventioninclude a variety of additives such as, for example, antistatic agents,blowing agents, delusterants, dye regulating agents, fillers, flameretardants, heat stabilizers, light stabilizers, lubricants, pigments,plasticizers, and combinations thereof. It is especially preferred toadd lubricants such as, for example, zinc stearate and calcium stearate,by the process of the present invention because of the problemsassociated with adding lubricants to the polymer melt stream beforeextrusion.

[0028] Referring now to the drawings, there is shown in FIG. 1a theapparatus of the present invention. The apparatus includes a dieassembly, a pumping system, and a distribution line. The pumping systemcomprises additive supply 10, recirculation pump 11, and metering pump12. Additive supply 10 may be a tank or an extruder. One or moreadditives is maintained at the proper temperature within additive supply10 and pumps 11, 12 using heat tracing and insulation (not shown). Ingeneral, pumps 11, 12 deliver the one or more additives to die assembly20 located at the end of extruder 60. More specifically, pump 11circulates the one or more additives from additive supply 10 to meteringpump 12, and any additive that is not taken away by metering pump 12 isreturned back to additive supply 10 by way of recirculation line 13. Therecirculation of the one or more additives provides ample pressure,i.e., from about 30 to about 5,000 psig, to feed inlet 14 of meteringpump 12. From metering pump 12, the one or more additives is transferredto die assembly 20 by means of distribution line 15, which may be heattraced, high-pressure tubing or piping. Die assembly 20, which will bedescribed in more detail below, preferably contains distribution plate21, thin-plate assembly 22, and die head plate 23 (FIGS. 2-4).Simultaneously, solid particles of polymer are fed into hopper 61 andflow from hopper 61 into extruder 60 where the polymer is extruded. Theextruded polymer melt flow is then fed to die assembly 20 where the oneor more additives is injected into one or more predetermined locationsalong the cross-section of the polymer melt flow as the melt flow passesthrough die assembly 20 and is shaped into strands.

[0029] In another embodiment, as seen in FIG. 1b, the pumping system canbe a weight loss feeder system such as those known in the art ofchemical dispensing. An example of a commercially available weight lossfeeder system is a K-Tron Soder liquid loss-in-weight feeder system madeby K-Tron International of Pitman, N.J. In this embodiment, additivesupply 10 is placed upon weight scale 70 that measures the weight ofadditive supply 10 and its liquid contents. A heated distribution line71 connects additive supply 10 to metering pump 12 without interferingwith the movement of the weight scale. Metering pump 12 delivers the oneor more additives to die assembly 20 (FIG. 1) via distribution line 15.A control system 72 calculates the loss in weight of additive supply 10over a given period of time, which is the metering pump delivery rate. Atime period of from 0 to 60 seconds is generally sufficient to provideaccurate flow delivery. The control system, therefore, can control thepump speed in order to provide the proper delivery rate of one or moreadditives to die assembly 20. Control system 72 may include weighttransmitter 73, weight loss controller 74, and metering pump drive motorinverter 75, which is connected to metering pump motor 76, metering pumpmotor gear box 77, and metering pump drive shaft 78.

[0030]FIG. 1c illustrates yet another embodiment of the pumping system.In this embodiment, a flow sensor may be used in place of the weightscale to measure the flow and to control the pump. As shown in FIG. 1c,heated distribution line 71 connects additive supply 10 to flow sensor79 and then to metering pump 12. Metering pump 12 delivers the one ormore additives to die assembly 20 (FIG. 1) via distribution line 15. Acontrol system 80 determines the flow rate, which is the metering pumpdelivery rate. The control system, therefore, can control the pump speedin order to provide the proper delivery rate of one or more additives todie assembly 20. Control system 80 may include flow transmitter 81, flowindicating controller 82, and metering pump drive motor inverter 75,which is connected to metering pump motor 76, metering pump motor gearbox 77, and metering pump drive shaft 78.

[0031] The thin-plate assembly used in the present invention contains atleast two thin plates. Each plate in the thin-plate assembly preferablyis as flat as possible and is free of scratches. The number of thinplates in the assembly will depend on the complexity of the componentdistribution desired in the final product. Typically, from 1 to about 5plates are used, although more plates can be used in the method andapparatus of this invention. Each thin plate typically has a thicknessof less than about 0.25 inch and, more preferably, of from about 0.001to about 0.10 inch.

[0032] The thin plates are preferably made from metal. Suitable metalsfor use in the thin plates include, for example, stainless steel,aluminum and aluminum-based alloys, nickel, iron, copper andcopper-based alloys, mild steel, brass, titanium, and othermicromachineable metals. Because it is relatively inexpensive, stainlesssteel is preferably used.

[0033] Each thin plate has a first facial surface and an opposite secondfacial surface, wherein on either or both of the first facial and secondfacial surfaces, multiple distribution paths are formed by an etching(or micromachining) process. The multiple distribution flow paths have aflow pattern effective to distribute and arrange the polymer melt flowand the one or more additives in a predetermined spatial configuration.The specific flow pattern will depend on the desired placement of theone or more additives into or on the polymer melt flow.

[0034] Typically, the multiple distribution flow paths in the thinplates are composed of multiple distribution flow channels and multipledistribution flow apertures (or “through holes”), wherein thedistribution flow channels have a lesser depth than the thickness of thethin plates, and further wherein the distribution flow aperturescommunicate between the first facial surface and the second facialsurface of the thin plates. Preferably, at least some of thedistribution flow apertures are in communication with respectivedistribution channels.

[0035] The multiple distribution flow paths are formed in the firstand/or second facial surfaces of the thin plates by etching (ormicromachining) processes such as, for example, photochemical and laseretching, stamping, punching, pressing, cutting, molding, milling,lithographing, particle blasting, reaming, or combinations thereof.According to the current preference, the flow paths may bephotochemically etched into the surfaces.

[0036] The advantages of thin plates are well known in the art andinclude, for example, relative ease in producing, cleaning, andinspecting the plates. Thin plates are also inexpensive, disposable,easily changeable, and capable of distributing and combining a pluralityof components in a predetermined configuration with respect to eachother.

[0037] As noted above, the configuration of thin-plate assembly 22 ofdie assembly 20 depends on the desired placement of the one or moreadditives in the polymer. While the number of through holes anddistribution channels in the thin plates varies, what follows aredescriptions of the preferred embodiments of the thin plates. FIG. 2 isan exploded view of one configuration of die assembly 20 used in theapparatus of the present invention. In this configuration, thin-plateassembly 22 is designed such that one or more additives may be placedinto the core of three separate polymer strands, as in a core/sheathconfiguration.

[0038] In FIG. 2, die assembly 20 has a thin-plate assembly 22 thatincludes thin plates 24, 25 sandwiched between distribution plate 21 anddie head plate 23. Dowel pin 16 is used to align thin plates 24, 25 withdistribution plate 21. Die assembly 20 is connected to the die head (notshown) of extruder 60 (FIG. 1) using a plurality of bolts 51.Distribution line 15 is connected to inlet connection 17 located on theside of die head plate 23 using a high-pressure tubing connector (tubingfitting) 18. Distribution line 15 may be high-pressure tubing or piping.Tubing connector 18 may also be a welded connector, threaded connector,or another commonly used connector. The one or more additives inmetering pump 12 (FIG. 1) is transferred to die assembly 20 viadistribution line 15 and enters die assembly 20 through inlet connection17 in die head plate 23. The one or more additives then flows throughhole 26 in die head plate 23, through hole 27 in thin plate 24, andthrough hole 28 in thin plate 25. At thin plate 25, the one or moreadditives hydraulically splits into three equal streams through threechannels 29, 30, 31 in thin plate 25. Channels 29, 30, 31, which are allof equal length, direct the additive streams into holes 32, 33, 34 inthin plate 25 and then into the cores of the three different strands ofthe polymeric host material via holes 35, 36, 37 in thin plate 24.Simultaneously, polymeric host material supplied from extruder 60 isdirected into central channel 38 of distribution plate 21. Distributionplate 21 divides the polymeric host material into three sections of fourpolymer streams each using distribution holes 39 a-d, 40 a-d, 41 a-dthat have been drilled into distribution plate 21. The polymer streamsthen flow through holes 42 a-d, 43 a-d, 44 a-d in thin plate 25 to thinplate 24 where the polymer streams are combined with the additivestreams using “X” patterns 45, 46, 47 in plate 24 to converge the fourseparate polymer streams in each region into a sheath of polymeric hostmaterial that surrounds an additive core.

[0039] In FIG. 3, there is shown an exploded view of a secondconfiguration of the thin-plate assembly 22 of die assembly 20. In thisconfiguration, thin-plate assembly 22 allows for placement of one ormore additives inside of each of three strands of the polymeric hostmaterial in an islands-in-a-sea arrangement. The one or more additivesin metering pump 12 (FIG. 1) is transferred to die assembly 20 viadistribution line 15 and enters die assembly 20 through inlet connection17 located on the side of die head plate 23. The one or more additivesthen flows through hole 26 in die head plate 23, through hole 27 in thinplate 24, and through hole 28 in thin plate 25 a where the one or moreadditives then hydraulically splits into three equal streams and flowsthrough channels 29, 30, 31 in thin plate 25 a. From each of channels29, 30, 31, the additive streams are transferred to distributionchannels 48, 49, 50 located around the regions of polymer holes 48 i-l,49 i-l, 50 i-l (FIG. 3a). Distribution channels 48, 49, 50 preferablyare spherical (e.g., circular, oval-shaped, ellipse-shaped, etc.),though any shape that allows for distribution of the additive streams iscontemplated. Next, from distribution channels 48, 49, 50, the additivestreams are transferred to channels 48 a-d, 49 a-d, 50 a-d (FIG. 3a).Channels 48 a-d, 49 a-d, 50 a-d, which are similar to spokes on a wheel,are of equal length. Channels 48 a-d, 49 a-d, 50 a-d direct the additivestreams from each of distribution channels 48, 49, 50 to holes 48 e-h,49 e-h, 50 e-h (FIG. 3a) in thin plate 25 a. The additive streams thenflow into holes 45, 46, 47 in thin plate 24 so that the additive steamsmay be placed as four islands in each of the polymer strands.Simultaneously, the polymeric host material supplied by extruder 60 isdirected into central channel 38 of distribution plate 21. Distributionplate 21 divides the polymer stream into three sections, each sectionhaving four polymer streams, using distribution holes 39 a-d, 40 a-d, 41a-d drilled into distribution plate 21. The polymer streams then flowthrough holes 48 i-l, 49 i-l, 50 i-l (FIG. 3a) in thin plate 25 a andare combined with the additive islands in thin plate 24. Thin plate 24has “X” patterns 45, 46, 47 that converge the four separate polymerstreams of each region to form the sea that encapsulates the fouradditive islands.

[0040]FIG. 4 shows yet another configuration of thin-plate assembly 22of die assembly 20 useful in the method and apparatus of the presentinvention. In FIG. 4, thin-plate assembly 22 is configured such that oneor more additives may be placed in a pattern of four stripes on thesurface of each polymer strand. The one or more additives in meteringpump 12 (FIG. 1) is transferred to die assembly 20 via high-pressuretubing or piping 15 and enters die assembly 20 through inlet connection17 located on the side of die head plate 23. The one or more additivesthen flows through hole 26 in die head plate 23 and hole 28 in thinplate 25 b where the one or more additives hydraulically splits intothree equal streams in channels 29, 30, 31 in thin plate 25 b. From eachof channels 29, 30, 31, the additive streams are transferred todistribution channels 48, 49, 50. Distribution channels 48, 49, 50preferably are spherical (e.g., circular, oval-shaped, ellipse-shaped,etc.), though any shape that allows for distribution of the additivestreams is contemplated. Next, from distribution channels 48, 49, 50,the additive streams are transferred to channels 48 a-d, 49 a-d, 50 a-d(FIG. 4a). Channels 48 a-d, 49 a-d, 50 a-d, which are similar to spokeson a wheel, are of equal length. Channels 48 a-d, 49 a-d, 50 a-d directthe additive streams around the outside of the polymer strand holes 32,33, 34. Simultaneously, the polymeric host material supplied by extruder60 is directed into central channel 38 of distribution plate 21.Distribution plate 21 divides the polymeric host material into threesections of four polymer streams each using distribution holes 39 a-d,40 a-d, 41 a-d drilled into distribution plate 21. The polymer streamsthen flow into “X” patterns 45, 46, 47 in thin plate 24 which convergethe four separate polymer streams of each region into a single polymerstrand before the additive stripes are added as the polymer strandpasses by thin plate 25 b.

[0041] With each thin-plate assembly, after the one or more additives isincorporated into the polymer melt flow, the strands of polymeric hostmaterial containing the one or more additives exit die assembly 20 andmay then pass through water bath 62 and into pelletizer 63, which cutsthe polymer strands into pellets or chips.

[0042] The invention will be further described by reference to thefollowing detailed examples. The examples are set forth by way ofillustration and are not intended to limit the scope of the invention.

EXAMPLE 1

[0043] A die containing a thin-plate assembly of the fourislands-in-a-sea configuration is designed to inject a low molecularweight lubricant (zinc stearate) into nylon 6 (Ultramid B3 availablefrom BASF Corporation of Mount Olive, N.J.), while the passing the nylon6 through a die and shaping it into strands for pelletizing. The zincstearate is injected into the nylon 6 having a relative viscosity (insulfuric acid) of 3.0. At the beginning of the experiment, the meteringpump is started a few minutes before the extruder to prevent the nylon 6from plugging up the holes in the thin plates for the zinc stearate. Thefollowing settings are used: Extruder: ZSK25 Werner & Pfleidererco-rotating twin screw Screw speed: 300 rpm Barrel temperature: 259° C.Die head temperature: 300° C. Extruder output: 20 kg/hour (333 g/minute)of nylon 6 Metering pump size: 0.16 cc/rev Metering pump temperature:150° C. Additive supply temperature: 150° C. Transfer tubingtemperature: 180° C.

[0044] Examination of the cross-section of the resulting polymer strandsshows that while the four islands appear to have collapsed into a singlecore, the zinc stearate is uniformly dosed along the length (i.e., inthe extrusion direction) of the cross-section but not mixed with thenylon 6 to form a single phase. The collapse of the four islands into asingle core is thought to be the result of the differences in theviscosity of the zinc stearate and the nylon 6, i.e., the componenthaving the lower viscosity migrates to the center.

EXAMPLE 2

[0045] A die containing a thin-plate assembly is designed to injectpolypropylene wax dyed with 1 percent Heliogenblue (blue dye) onto thesurface and into the melt core of polystyrene 168N strands. The thinplate assembly for samples 2 and 3 is a sheath/core configuration, andthe thin plate assembly for samples 4 and 5 is a four stripesconfiguration. At the beginning of the experiment, the metering pump isstarted a few minutes before the extruder to prevent the polystyrene168N from plugging up the distribution holes in the thin plates for thepolypropylene wax. The following settings are used: Extruder: ZSK25Werner & Pfleiderer co-rotating twin screw Screw speed: 300 rpm Barreltemperature: 250° C. Die head temperature: 300° C. Extruder output: 30kg/hour (500 g/minute) of polystyrene 168N Metering pump size: 0.16cc/rev Metering pump temperature: 150° C. Additive supply temperature:130° C. Transfer tubing temperature: 170° C.

[0046] Examination of the cross-sections of the resulting polymerstrands of samples 2 and 3 shows two separate domains, a “star-shaped”core domain of polypropylene wax surrounded by a nylon 6 sheath domain.The “star-shaped” core is thought to be caused by the viscositydifferences between polystyrene 168N and polypropylene wax.

[0047] Examination of the cross-sections of the resulting polymerstrands of samples 4 and 5 indicates four stripes of polypropylene waxon the outside surface of the polystyrene core.

EXAMPLE 3

[0048] A die containing a thin-plate assembly is designed to inject alow molecular weight lubricant (zinc stearate) into nylon 6 (Ultramid B3supplied by BASF Corporation of Mount Olive, N.J.), while passing thenylon 6 through a die and shaping it into strands for pelletizing. Thethin plate assembly for samples 6 and 7 is a four stripes configuration,and the thin plate assembly for sample 8 is a four islands-in-a-seaconfiguration. At the beginning of the experiment, the metering pump isstarted a few minutes before the extruder to prevent the Ultramid B3polymer from plugging up the distribution holes in the thin plates forthe zinc stearate. The following settings are used: Extruder: ZSK25Werner & Pfleiderer co-rotating twin screw Screw speed: 300 rpm Barreltemperature: 260° C. Die head temperature: 260° C. Extruder output: 30kg/hour (500 g/minute) of Ultramid B3 Metering pump size: 0.16 cc/revMetering pump temperature: 140° C. Additive supply temperature: 130° C.Transfer tubing temperature: 140° C.

[0049] Examination of the cross-sections of the resulting polymerstrands of samples 6 and 7 indicates four stripes of zinc stearate onthe outside surface of the nylon 6 core. Sample 8 produced across-section having a single core of zinc stearate in the center of thecross-section surrounded by a sheath of nylon 6, as in Example 1.

[0050] While the invention has been described in connection with what ispresently considered to be the most practical and preferred embodiment,it is to be understood that the invention is not to be limited to thedisclosed embodiment, but on the contrary, is intended to cover variousmodifications and equivalents arrangements included within the spiritand scope of the appended claims.

What is claimed is:
 1. A method of directing at least one additive to across-section of a host polymeric melt flow comprising the steps of: (a)supplying a melt flow of a polymeric host material to a die assemblycomprising a thin-plate assembly; and (b) injecting at least oneadditive into at least one predetermined location in a cross-section ofthe melt flow of the polymeric host material while passing the melt flowof the polymeric host material through the die assembly, wherein the atleast one additive is injected into the at least one predeterminedlocation in the cross-section of the melt flow of the polymeric hostmaterial to achieve uniform dosing of the additive in the extrusiondirection in the at least one predetermined location of thecross-section of the polymeric host material.
 2. The method of claim 1 ,wherein the thin-plate assembly comprises at least a first thin plateand a second thin plate, the first thin plate having channels formed ona surface thereof.
 3. The method of claim 1 , wherein the polymeric hostmaterial is selected from the group consisting of polyamides,polyesters, polystyrene, acrylics, polyolefins, and combinationsthereof.
 4. The method of claim 3 , wherein the polymeric host materialis polyamide.
 5. The method of claim 4 , wherein the polyamide is nylon6.
 6. The method of claim 1 wherein the additive is selected from thegroup consisting of antistatic agents, blowing agents, delusterants, dyeregulating agents, fillers, flame retardants, heat stabilizers, lightstabilizers, lubricants, pigments, and plasticizers and combinationsthereof.
 7. The method of claim 1 , wherein the additive is a lubricant.8. The method of claim 7 , wherein the lubricant is selected from thegroup consisting of zinc stearate and calcium stearate.
 9. The method ofclaim 1 , wherein the additive is placed into the core of the melt flowof the polymeric host material.
 10. The method of claim 1 , wherein theadditive is placed into the melt flow of the polymeric host material inan islands-in-a-sea arrangement.
 11. The method of claim 1 , wherein theadditive is placed in a pattern of stripes on the surface of the meltflow of the polymeric host material.
 12. An apparatus for injecting atleast one additive directly into a cross-section of a host polymer meltflow comprising: (a) a pumping system; (b) a die assembly comprising athin-plate assembly, wherein the thin-plate assembly comprises at leasta first thin plate and a second thin plate, the first thin plate havingchannels formed on a surface thereof; and (c) a first distribution line.13. The apparatus of claim 12 , wherein the pumping system comprises anadditive supply, a recirculation pump, and a metering pump.
 14. Theapparatus of claim 12 , wherein the pumping system comprises an additivesupply, a weight scale, a metering pump, and a second distribution line.15. The apparatus of claim 12 , wherein the pumping system comprises anadditive supply, a flow sensor, a metering pump, and a seconddistribution line.
 16. The apparatus of claim 12 , wherein the firstdistribution line comprises heat traced, high-pressure tubing.
 17. Theapparatus of claim 12 , wherein the die assembly further comprises adistribution plate and a die head plate, the thin plates being locatedbetween the distribution plate and the die head plate.
 18. A method ofmaking pellets from at least one polymeric host material comprising thesteps of: (a) supplying a melt flow of at least one polymeric hostmaterial to a die assembly comprising a thin-plate assembly; (b)directing the injection of at least one additive in at least onepredetermined location in a cross-section of the melt flow of thepolymeric host material while passing the melt flow through the dieassembly to form polymer strands, wherein the at least one additive isinjected into the at least one predetermined location in thecross-section of the melt flow of the polymeric host material to achieveuniform dosing of the additive in the extrusion direction in the atleast one predetermined location of the cross-section of the polymerichost material; and (c) cutting the polymer strands to form pellets. 19.The method of claim 18 , wherein the thin-plate assembly comprises atleast a first thin plate and a second thin plate, the first thin platehaving channels formed on a surface thereof.
 20. The method of claim 18, wherein the polymeric host material is selected from the groupconsisting of polyamides, polyesters, polystyrene, acrylics,polyolefins, and combinations thereof.
 21. The method of claim 18 ,wherein the polymeric host material is polyamide.
 22. The method ofclaim 21 , wherein the polymeric host material is nylon
 6. 23. Themethod of claim 18 , wherein the additive is selected from the groupconsisting of antistatic agents, blowing agents, delusterants, dyeregulating agents, fillers, flame retardants, heat stabilizers, lightstabilizers, lubricants, pigments, and plasticizers and combinationsthereof.
 24. The method of claim 23 , wherein the additive is alubricant.
 25. The method of claim 24 , wherein the lubricant isselected from the group consisting of zinc stearate and calciumstearate.
 26. The method of claim 18 , wherein the additive is placedinto the core of the melt flow of the polymeric host material.
 27. Themethod of claim 18 , wherein the additive is placed into the melt flowof the polymeric host material in an islands-in-a-sea arrangement. 28.The method of claim 18 , wherein the additive is placed in a pattern ofstripes on the surface of the melt flow of the polymeric host material.29. A thin plate having formed on a surface thereof at least one firstchannel defining a perimeter about a center and having in fluid flowcommunication therewith at least one second channel radiating from saidfirst channel toward said center and terminating in at least one throughhole.
 30. A thin plate according to claim 29 , wherein said at least onefirst channel is spherical.
 31. A thin plate according to claim 30 ,wherein said at least one first channel is circular.
 32. A thin plateaccording to claim 29 , wherein two or more second channels radiate fromsaid first channel.
 33. A thin plate according to claim 32 , whereinsaid two or more second channels terminate in a single through hole. 34.A thin plate according to claim 32 , wherein each of said two or moresecond channels terminate at a separate, respective through hole.
 35. Athin plate according to claim 29 , wherein four-second channels radiatefrom said first channel.
 36. A thin plate according to claim 35 ,wherein said four channels terminate in a single through hole.
 37. Athin plate according to claim 35 , wherein each of said four channelsterminate at its own through hole.
 38. A pellet comprising a polymerichost material with an additive embedded therein, said additive selectedfrom the group consisting of antistatic agents, blowing agents,delusterants, dye regulating agents, fillers, flame retardants, heatstabilizers, light stabilizers, lubricants, pigments, and plasticizersand combinations thereof, wherein the additive is uniformly dosed, inthe extrusion direction, in the cross-section of the pellet in at leastone predetermined location.
 39. A pellet according to claim 38 , whereinthe additive is a lubricant.
 40. The pellet of claim 39 , wherein thelubricant is selected from the group consisting of zinc stearate andcalcium stearate.
 41. The pellet of claim 40 , wherein the additivedomain comprises the core of the pellet.
 42. The pellet of claim 40 ,wherein the polymeric host material and the additive are in anislands-in-a-sea arrangement and the additive comprises the islands inthe sea of the polymeric host material.
 43. The pellet of claim 40 ,wherein the additive domain comprises stripes on the surface of thepolymeric host material.
 44. A pellet according to claim 38 , whereinthe polymeric host material is selected from the group consisting ofpolyamides, polyesters, polystyrene, acrylics, polyolefins, andcombinations thereof.
 45. The pellet of claim 44 , wherein the polymerichost material is polyamide.
 46. The pellet of claim 45 , wherein thepolyamide is nylon 6.